In recent years it has become a kind of fashion - especially in those countries, such as Germany and Poland, that suffered most directly from the ideological excesses of the mid-20th century - to excavate, point fingers and take the moral high ground. Rootling in long-closed files makes for good, titillating copy; it is generally couched in terms of truth-seeking and boil-lancing, and in some senses genuinely is. However, it is also worth asking questions about the relevance now of some of these discoveries, and whether they should be allowed to overshadow entire lives; but also, as Timothy Garton Ash argued recently in this paper, to work out exactly what the context and reality was at the time, and to understand precisely what present-day agendas are behind how these revelations are discussed.

Last year the subject/scapegoat was Günther Grass, who to some extent forestalled the finger-pointers by writing in his autobiography of his short-lived service in the SS; now it is the turn of the eminent Polish sociologist Zygmunt Bauman. An article in the rightwing Polish magazine Ozon, by historian Bogdan Musial, has alleged that Bauman, who has lived and taught in Leeds for over 35 years, was for a while in the pay of the Polish secret service, and that he participated in the political cleansing of opponents of the regime. The story has been picked up, heatedly, in Germany, where his work is much revered. Andreas Hess, a lecturer in sociology, repeated it in the Irish Times. Bauman has two books being published in the UK at the moment, and it seems a good idea to ask for his side of the story.

"Look, I won't dignify Musial with an answer," says Bauman, his face contracting and his voice deepening, and answering anyway. "I don't want to give weight or importance to something which is [composed of] half-truths and 100% lies. What is true in his article is not new, because everybody knew I was a communist" - from 1946 to 1967 - "and that I served also for several years in the 'internal army', so called." The only new fact, he says, is that he did join the secret service, but only for three years, when he was 19, and for this "I bear full responsibility."

It is a response of a piece with his ideas, one of which is that modernity has created the perfect conditions for individuals to act unethically; and that taking personal responsibility and acting morally is a greater test than it has ever been before. So, in Modernity and the Holocaust (1989), he argued that complicity in the Final Solution was not a product specifically of Nazism, or of an unusual coming-together of evil people, but of a modern system, an intricate bureaucracy in which obedience to superiors was prized above all, and whose layers partially obscured to ordinary people the consequences of their actions.

In nearly 50 books (25 of them published since he retired from teaching in 1990) he has devoted himself to understanding the society we live in, and in the process has become one of the most highly esteemed social critics in Europe.

Bauman's particular achievement has been to mount a sustained critique of totalitarianism while at the same time, like some of the thinkers he admires, such as Richard Rorty and Richard Sennett, retaining an essentially socialist belief in the ethical necessity of equality and justice. Increasingly he has also been a critic of the Third Way, and of globalisation. So Consuming Life, to be published next month, argues that our consumerist society, in which everything is judged according to its market value, and discarded if found wanting, applies, with terrible consequences, to our most intimate relationships as well. Why commit to a relationship if you can always bin it and try another one? We are losing our ability to "establish firm, solid, reliable and satisfaction-bringing relationships with other people," he says.

Bauman was born in Poznan, Poland, in 1925, so he was a teenager when the Germans invaded. His family caught the last train east to Russia. When he was old enough he joined the Fourth Division of the Polish exile army in Russia - not the Red Army, as is usually reported - with whom he entered Poland.

"Poland was a very backward country before the war, which was exacerbated by the occupation. In an impoverished country you expect deprivation, humiliation, human indignity and so on, a whole complex of social and cultural problems to be dealt with. If you looked at the political spectrum in Poland at that time, the Communist party promised the best solution. Its political programme was the most fitting for the issues which Poland faced. And I was completely dedicated. Communist ideas were just a continuation of the Enlightenment."

And so, at 19, "when I hadn't even started my life", he became a member of the Communist party, and, by an accident of history, he says - because the Fourth Division was co-opted for the job, rather than, say, the second or third - became a member of the "internal army" - the force charged with "suppressing terrorism inside the country - the equivalent of that fashionable phrase now, 'the war against terrorism'. This is public knowledge - everybody knew that. I never hid it." He wrote political pamphlets for soldiers. "My job there was very dull, in fact."

"The fact that I for three years cooperated with intelligence - well, that's the only thing I never said." What did that involve, exactly? "Well, it's counter-espionage. Every good citizen should participate in counter-espionage. That was one thing that I kept secret, because I signed an obligation that it would be kept secret ... So that's the only thing. All the other 'news', so called, is completely in error."

Did counter-espionage mean informing on people who were fighting against the communist project? "That's what would be expected from me, but I don't remember doing [anything like that]. I had nothing to do - I was sitting in my office and writing - it was hardly a field in which you could collect interesting information." Did you do anything at all that might have had adverse consequences? "I can't answer that question," he says, upset now. "I don't believe there was any. At the same time, I was a part of a wider scene, and of course everything you do has consequences." What else did Musial's article get wrong? "Everything else. For example - just to give you an example - no. I really don't want to speak about it, because you've pushed me into doing exactly what I didn't want to do, assigning significance to something which is irrelevant."

Bauman soon quit the secret service, and as for the Communist party, "gradually, like so many others in my position, I came to the conclusion that there was a yawning gap between the official word and the practice ... so I became a revisionist, rejecting the official version of Marxism."

He would pay dearly for his apostasy. "The thing that is completely missing from the stories is that though I cooperated for two, three years, I was the object of persecution from the secret services for 15 years. Immediately afterwards, I was spied on, I was reported on, I had my flat bugged, my telephone was bugged, and so on. I was thrown away from the internal army, and in the end, as you know, I was expelled from the university, expelled from any ability to publish." An anti-semitic purge in 1968 meant that both he and his wife Janina lost their jobs. A mirthless laugh. "If the author of this lampoon was really working in the archives he'd probably discover that the files dedicated to me as the enemy are much thicker than the files dedicated to me as a collaborator. But I wouldn't expect balance from him ... I feel more like a victim, really, in this case." They joined their daughter in Israel, but he was not a Zionist, and they felt uncomfortable. By the time they arrived in Leeds they were in their 40s.

He sees his "outing" as part of a new kind of witch-hunt under way in Poland, a process of legitimisation for the rightwing government of Lech and Jaroslaw Kaczynski. "I think that's the explanation - I have never made a secret that I am a socialist. I was leftwing, I am leftwing, and I will die leftwing. Hopefully. So by discrediting me they may obliquely discredit the political left in Poland." And it is true that the brothers, who see themselves as moral patriots stamping out the remnants of communism, seem to be following a policy of disclosure and systematic file-leaking that involves vetting hundreds of thousands of people, a number of whom stand to lose their jobs. Some may well have done things for which they deserve to be called to account, but the atmosphere is reportedly poisonous. Bauman's treatment is thus, he says, "explicable in terms of a certain context ... That's what's going on. Nothing particularly novel about it, nothing very sensational, it's just how things are."

Does he think those three years were a mistake? "They're part of my biography. I bear full responsibility for that. At that time it seemed to me the right thing to do ... Some choices in everybody's biography can be looked upon as wrong choices, except that it doesn't seem to be a wrong choice at that time. When I was 19 years old I didn't know as much as I know now that I'm 82."